ytdlp-segment-downloader/src/cli/downloader.ts

import { spawn } from "child_process";
import { writeFileSync, mkdirSync, existsSync } from "fs";
import { join } from "path";

export interface DownloadOptions {
  url: string;
  outputDir: string;
  format: string;
  extractChapters: boolean;
}

interface Chapter {
  title: string;
  start: number;
  end: number;
}

async function getVideoInfo(url: string): Promise<{ title: string; chapters: Chapter[] }> {
  return new Promise((resolve, reject) => {
    const ytDlp = spawn("yt-dlp", [
      "--dump-json",
      "--no-download",
      url,
    ]);

    let stdout = "";
    let stderr = "";

    ytDlp.stdout.on("data", (data) => {
      stdout += data.toString();
    });

    ytDlp.stderr.on("data", (data) => {
      stderr += data.toString();
    });

    ytDlp.on("close", (code) => {
      if (code !== 0) {
        reject(new Error(`yt-dlp failed: ${stderr}`));
        return;
      }

      try {
        const info = JSON.parse(stdout);
        const chapters: Chapter[] = [];

        if (info.chapters && Array.isArray(info.chapters)) {
          for (const chapter of info.chapters) {
            chapters.push({
              title: chapter.title || `Chapter ${chapters.length + 1}`,
              start: chapter.start_time || 0,
              end: chapter.end_time || 0,
            });
          }
        }

        resolve({
          title: info.title || "video",
          chapters,
        });
      } catch (parseError) {
        reject(new Error(`Failed to parse video info: ${parseError}`));
      }
    });

    ytDlp.on("error", (err) => {
      reject(new Error(`Failed to run yt-dlp: ${err.message}`));
    });
  });
}

async function downloadSection(
  url: string,
  outputPath: string,
  section: string,
  format: string
): Promise<void> {
  return new Promise((resolve, reject) => {
    const ytDlp = spawn("yt-dlp", [
      "-f", format,
      "--download-sections", section,
      "-o", outputPath,
      url,
    ]);

    let stderr = "";

    ytDlp.stderr.on("data", (data) => {
      stderr += data.toString();
    });

    ytDlp.on("close", (code) => {
      if (code !== 0) {
        reject(new Error(`yt-dlp failed: ${stderr}`));
        return;
      }
      resolve();
    });

    ytDlp.on("error", (err) => {
      reject(new Error(`Failed to run yt-dlp: ${err.message}`));
    });
  });
}

function sanitizeFilename(filename: string): string {
  return filename
    .replace(/[^a-zA-Z0-9\s\-_]/g, "")
    .replace(/\s+/g, "_")
    .substring(0, 100);
}

function formatTime(seconds: number): string {
  const mins = Math.floor(seconds / 60);
  const secs = Math.floor(seconds % 60);
  return `${mins}:${secs.toString().padStart(2, "0")}`;
}

export async function downloadVideoSegments(options: DownloadOptions): Promise<void> {
  const { url, outputDir, format } = options;

  // Create output directory if it doesn't exist
  if (!existsSync(outputDir)) {
    mkdirSync(outputDir, { recursive: true });
  }

  // Skip chapter extraction if not requested
  if (!options.extractChapters) {
    console.log("Downloading full video (chapters disabled)...");
    const safeTitle = sanitizeFilename("video");
    const outputPath = join(outputDir, `${safeTitle}.%(ext)s`);
    await downloadSection(url, outputPath, "*", format);
    return;
  }

  // Get video info including chapters
  console.log("Fetching video information...");
  const { title, chapters } = await getVideoInfo(url);
  const safeTitle = sanitizeFilename(title);

  console.log(`Video: ${title}`);
  console.log(`Found ${chapters.length} chapters\n`);

  if (chapters.length === 0) {
    console.log("No chapters found. Downloading full video...");
    const outputPath = join(outputDir, `${safeTitle}.%(ext)s`);
    await downloadSection(url, outputPath, "*", format);
    return;
  }

  // Download each chapter as a separate segment
  for (let i = 0; i < chapters.length; i++) {
    const chapter = chapters[i];
    const segmentNumber = (i + 1).toString().padStart(2, "0");
    const outputPath = join(outputDir, `${safeTitle}_${segmentNumber}_${sanitizeFilename(chapter.title)}.%(ext)s`);
    const section = `*${formatTime(chapter.start)}-${formatTime(chapter.end)}`;

    console.log(`[${i + 1}/${chapters.length}] Downloading: ${chapter.title} (${formatTime(chapter.end - chapter.start)})`);

    await downloadSection(url, outputPath, section, format);
  }

  // Also download the full video
  console.log("\nDownloading full video...");
  const fullVideoPath = join(outputDir, `${safeTitle}_full.%(ext)s`);
  await downloadSection(url, fullVideoPath, "*", format);

  // Save chapter list
  const chapterListPath = join(outputDir, `${safeTitle}_chapters.txt`);
  let chapterList = `# ${title}\n\n`;
  for (const chapter of chapters) {
    chapterList += `${formatTime(chapter.start)} - ${chapter.title}\n`;
  }
  writeFileSync(chapterListPath, chapterList);
  console.log(`Chapter list saved to: ${chapterListPath}`);
}